Remote sensing of the depth of a liquid, for example, in a tailings pond, river, stream, lake or pond, brings with it special challenges. There are many methods of measuring depth of a body of liquid. Some of these rely upon pressurizing a pipe or tube that has an outlet at the depth to be measured such that the pressure in the tube is proportional to the depth of the liquid at the outlet. The pressurized gas source is located at or above the surface. Such methods are not suitable for remote sensing.
Historically, a nitrogen tank, regulator and needle valve to regulate the gas flow have been used. This relied upon a human to operate the needle valve and hence could be done in remote locations, but not remotely.
More recently, the nitrogen tank was replaced with a compressor run on solar power or battery power and the needle valve was replaced with a pressure differential across an orifice. While this allowed for remote sensing, it led to new challenges. First is that the pressure from the compressor is not very tightly controlled. The solution to this problem is to use a valve with a very small orifice. The problem that arises from this is that the orifice can be easily partially or completely occluded. Another problem is that if a fixed orifice valve is used, it requires calibration because there is significant variability in the size of a fixed orifice that must be measured during manufacturing to calibrate the air flow for a given pressure differential. The prior art fails to address these challenges.
For example, United States Patent Application 20030140697 discloses a liquid depth sensing system utilizing the bubble tube or purge operating principle. In this system, a pneumatic tube extends downwardly into the liquid, and air (or other gas) passes through the tube to bubble from the lower end thereof. The air or gas pressure within the tube is equal to the head pressure of the liquid, thus allowing the liquid depth to be determined by measuring the air or gas pressure. The technology uses a pneumatic pump motor as the regulating device, by operating the motor only as required to produce only sufficient pressure for measuring the liquid depth. In some embodiments, a regulator valve provides adjustment of the output flow from the pump for additional accuracy. In other embodiments, a differential pressure transducer provides feedback to the motor controller to preclude requirement for the regulator valve. This application does not contemplate nor solve the problem of a partially or fully occluded orifice or the need for calibration.
U.S. Pat. No. 8,756,991 discloses a pneumatic sensor/indicator device that includes a sensor assembly having a bellows receiving chamber and sensor housing. An elastic bellows is in the bellows receiving chamber. A shaft connects to the bellows so bellows extension/retraction causes shaft axial movement. A magnet connected to the shaft generates a field moving an indicator ring. An indicator dome connects to the sensor body. The indicator ring is in the sensor housing in a non-indicating condition and displaces into the indicator dome providing a visible indicating condition. A flexible sensor tube connected to the sensor/indicator device extends into a well tube having a level sensing tube extending therefrom. A well fluid level rising above a level sensing tube inlet end increases inlet pressure port pressure inducing bellows axial displacement causing indicator device movement toward the indicating condition. The dome and indicating ring are isolated from the well preventing well contents entering and fogging the dome. This technology is specific to wells. It is not suited to remote sensing as a user is required to view the sensor output on site.
U.S. Pat. No. 8,521,452 discloses a liquid level determination system that includes pressure determination components that include an interference dampener to mitigate interference originating from a bubbler air compressor. The system may include a pressure pipe with a pressure sensing pipe end located adjacent to the pressure determination components and a bubbler pipe end locatable at least partially in a wet well. The wet well may include a pump that has a volute. The pressure pipe may further include layered pipe sections, and the position of the bubbler pipe end may be calculated so that it is not lower than a level substantially equivalent to a center line through the volute. The bubbler air compressor may provide air pressure to the pressure pipe. The technology is focused on an interference damper to mitigate interference originating from a bubbler air compressor, such as oscillations in pressure. The transducer has an orifice of about 3 to 7 microns. The solution appears to be through a computer programme and also a sensor plug. It does not address the issue of a fully or partially occluded orifice or calibration.
U.S. Pat. No. 8,340,929 discloses a liquid level determination system to determine the level of a liquid in a wet well. The system may include pressure determination components and a pressure pipe with a pressure sensing pipe end located adjacent to the pressure determination components and a bubbler pipe end locatable at least partially in the wet well. A transducer is used to determine a pressure level within the pressure pipe maintained by a bubbler air compressor. A level detection processor may analyze the pressure level to determine a liquid level in the wet well. An interference dampener is included to mitigate interference originating from the bubbler air compressor. The interference dampener may be provided by transducer plug to restrict air flow. Alternatively, the interference dampener may be provided by a computer operated program to monitor and mitigate the interference. The technology does not consider, nor solve the problem of a fully or partially occluded orifice or calibration.
U.S. Pat. No. 7,895,890 discloses a liquid depth sensing and identification system that determines both the pressure head or depth, and therefore the quantity, of a liquid in a tank, as well as determining the characteristics of the liquid at the bottom of the probe. Two principles of operation are disclosed herein. The system may use a gas bubble collector about the outlet end of the purge tube, with the difference in height of the collector and purge tube mouths defining the very small difference in pressure head required to resolve the bubble emission characteristics produced in different liquids. Alternatively, the system incorporates a mass flow sensor capable of detecting minute changes in mass flow as bubbles are emitted from the purge tube in order to determine the type and characteristics of the liquid. The system operates using an open loop principle of operation, with no feedback provided to control the purge pump. This technology does not consider nor solve the problem of a fully or partially occluded orifice or calibration.
U.S. Pat. No. 5,983,716 discloses a procedure for measuring hydrostatic pressure, especially that of ground water, with the particularity that air is bubbled into the ground water, the pressure in the measuring pipe is fed to an absolute pressure cell and atmospheric pressure is then applied to the same measurement cell. It includes a valve that opens and closes but in response to the position of pistons that deliver pressurized air into the system to provide the bubbles. This is old technology that is not suitable for remote sensing.
U.S. Pat. No. 5,047,124 discloses an apparatus for feeding gas into a heated saline solution for pressure measurement or to pump this solution. The gas is introduced into the solution through a gas bubbling-in pipe having a gas outlet opening. The gas is heated prior to being introduced into the solution and is charged with moisture until the saturation of the gas comes close to or corresponds to the saturation conditions in the solution at the gas outlet opening. This minimizes clogging caused by crystallization at the feeder pipes carrying the measuring or purge gas. This technology is providing one solution to clogging, but at the gas outlet. The patent discloses that wider tubing can be used. This unfortunately reduces the accuracy of the measurements.
What is needed is a system and method that allows for accurate and reliable remote sensing of the depth of liquids. The system will preferably reduce or eliminate the need for calibration, will be robust enough for many environmental conditions and will preferably reduce or eliminate clogging, while remaining highly accurate. It should preferably be minimally affected by variations in gas pressure from the compressor.